1. Field of the Invention
The present invention relates to a liquid container that contains a liquid, such as ink or the like, to a head cartridge having the liquid container, to an ink jet printing apparatus that can print an image using the liquid container, and to a stirring method for the liquid container.
2. Description of the Related Art
In a serial type ink jet printing apparatus, a printing head that can eject ink, and an ink tank that contains ink to be supplied to the printing head are mounted on a carriage that can move in a main scanning direction. During image printing, an operation to eject ink from an ejection port of the printing head toward a printing medium while moving the carriage in the main scanning direction and an operation to transport the printing medium in a sub scanning direction crossing the main scanning direction are repeatedly performed. Then, ink droplets ejected from the printing head land on the printing medium, thereby printing a predetermined image.
As ink that is used in such an ink jet printing apparatus, there is known ink that contains a dye as a colorant. However, dye ink generally has slightly low light resistance and gas resistance. Accordingly, in case of a special use, such an outdoor notice, a printed matter with the dye ink rarely provides sufficient durability, that is, sufficient image solidity.
In recent years, a printing apparatus that uses ink containing a pigment as a colorant has been provided. The pigment ink has excellent light resistance and gas resistance, and thus a printed matter with the pigment ink can provide sufficient image solidity. However, unlike the dye ink, the pigment ink needs to be handled in consideration with colorant dispersibility. In order to obtain a uniformly printed image, it is necessary to disperse the colorant in a solvent.
Pigment particles in the pigment ink are floating in a dispersed state without being dissolved in an ink solution, unlike dye particles of the dye ink. If an ink tank containing the pigment ink stands still for a while, the pigment particles in the ink tank gradually settle by gravity, and a gradient of pigment particle concentration may occur in a height direction of the ink tank. That is, a high concentration layer of the colorant is located at the bottom of the ink tank, and a low concentration layer of the colorant is located at the top thereof. In this state, when ink is supplied from the ink tank to the printing head so as to start an image printing operation and then the printing operation is continued, a difference in density between images at the initial stage and the subsequent stage of the printing operation may occur.
For detailed explanation, it is assumed that an ink jet printing apparatus supplies ink from the bottom of the ink tank to the printing head. If an ink tank having a gradient of pigment particle concentration is mounted on the printing apparatus and a printing operation starts, since ink having high concentration layer of a colorant at the bottom of the ink tank is supplied at the initial stage of the printing operation, an unnecessarily high density image is printed. Thereafter, if the printing operation is continued, an image printing density is gradually lowered as ink in the ink tank is consumed. Then, in a state where the amount of ink in the ink tank becomes small, only ink having lower concentration of the colorant than an original concentration remains. For this reason, even if the images are printed on the basis of the same image data as that at the initial stage of the printing operation, the printing density is lowered. In particular, when the size or specific gravity of the pigment particle is large, the pigment particles markedly tend to settle. Accordingly, even if the ink tank is kept unused for a few days, a concentration gradient may occur to such a degree to affect an image.
As such, when the ink tank is used and then the concentration of the colorant of the ink to be ejected from the printing head is changed, a difference in density between the printed images at the initial use stage and the subsequent use stage of the ink tank occurs. In addition, for example, in a color ink jet printing system that uses a plurality of color inks and represents a color on the basis of a predetermined color balance, a color balance may deteriorate. In this case, a considerable difference in image density is recognized.
In order to maintain color density of ink droplets to be ejected from the printing head in a predetermined density range, regardless of the amount of ink remaining in the ink tank, it is preferable that the pigment particles in the ink tank can be uniformly dispersed during at least the printing operation.
In order to realize uniform dispersion of the pigment particles, there is suggested an ink tank that has a stirring member for stirring the pigment particles therein.
Japanese Patent Laid-Open No. 2005-066520 discloses an ink pack that includes a manually operable stirring body. The stirring body has a shape to be inserted into the ink pack from the outside. A part of the stirring body that protrudes outward serves as an operation portion for operating a stirring portion of the stirring body, which extends in the ink pack. That is, when a user swings the stirring portion regularly or if necessary, ink in the ink pack is stirred, such that the pigment particles can be dispersed.
Japanese Patent Laid-Open No. 2005-066520 also discloses an ink cartridge that includes a stirring member for stirring ink in the ink tank using an inertial force when a carriage moves during the printing operation. In Japanese Patent Laid-Open No. 2005-066520, as an example, a stirring body that is formed integrally with an ink cartridge case is shown. In this example, the stirring body extends to suspend from the top of the ink cartridge case to the bottom thereof, and a cylindrical weight portion is formed at a lower end of the stirring body. The stirring body is swung in the movement direction of the carriage with a basic portion at the top as a fulcrum by an inertial force according to an acceleration/stop/reverse operation of the carriage, thereby stirring ink in the ink cartridge.
Japanese Patent Laid-Open No. 2005-066520 also discloses a stirring bogy that can freely move at the bottom of the ink cartridge without being fixed to the ink cartridge case. The stirring body moves at the bottom of the ink cartridge by an inertial force according to the acceleration/stop/reverse operation of the carriage, thereby stirring ink.
Japanese Patent Laid-Open No. 2004-216761 discloses a stirring mechanism that includes a shaft-like weight and a plurality of fins. The shaft-like weight swings horizontally around a center axis of swing by an inertial force according to a movement of the carriage, and the fins are formed integrally with the shaft-like weight and swung horizontally. According to this configuration, since the plurality of fins are arranged in parallel in a height direction of the ink cartridge, ink is uniformly stirred from an upper layer to a lower layer in the ink cartridge.
However, in the configuration described in Patent Documents described above, since a stirring region is limited, there is a difficulty in stirring the settled pigment particles over the entire inside of the container, and thus efficiency is degraded.
For example, in the ink cartridge, which includes the manual stirring member, described in Japanese Patent Laid-Open No. 2005-066520, since a degree of freedom of movement of the stirring member is low, only ink in a limited region of the ink cartridge can be stirred. In particular, in the vicinity of a connection portion of the stirring body and the ink cartridge serving as the fulcrum of the stirring portion, a movement range of the stirring portion is narrow, and thus a sufficient stirring effect is not obtained.
In the stirring body, which is provided with the cylindrical weight portion, disclosed in Japanese Patent Laid-Open No. 2005-066520, the inertial force is efficiently used, but a stirrable range is insufficient. In addition, when the stirring body that can freely move at the bottom of the ink cartridge is used, ink in the vicinity of the bottom of the ink cartridge can be expected to be sufficiently stirred, but an upper region of the cartridge distant from the stirring body cannot be expected to be sufficiently stirred.
Meanwhile, in the stirring mechanism disclosed in Japanese Patent Laid-Open No. 2004-216761, since the plurality of fins are arranged in the height direction of the ink cartridge, stirring uniformity in the height direction can be expected to some extent. However, since the swing amount of the fins in the vicinity of the central axis in the ink cartridge is small, a stirring effect is small. Further, since the stirring member including the plurality of fins or a rotation shaft has a complex configuration, the ink cartridge itself becomes expensive.
As described above, since the pigment particles of the pigment ink in the ink cartridge gradually settle due to gravity, a gradient of pigment particle concentration occurs in the height direction of the ink cartridge. In order to eliminate the difference in concentration in the ink cartridge, it is effective to stir ink such that the high concentration ink settling at the lower layer of the ink cartridge is raised or the low concentration ink in the upper layer thereof flows into the lower layer.